The present invention relates to high performance high speed blades and, more particularly, to a turbine blade construction.
Blades of, for example, turbines or the like, represent the most important components of the components of a rotary machine in determining turbine efficiency and, consequently, the turbine blade construction has considerable influence on the performance of an electrical power generating plant. Thus, over the years, a number of studies have been conducted in an effort to determine the manner in which the efficiency of a power generating plant can be increased by improving the turbine blade construction.
The aim underlying the present invention essentially resides in providing a turbine blade structure of a high performance which reduces a downstream velocity defect of a turbine blade.
In accordance with advantageous features of the present invention, a turbine blade having a low blade profile loss is provided wherein a crossing point of an inlet angle .alpha..sub.1 and an outlet angle .alpha..sub.2 of the blade is located in a position in which a distance between a crossing point of an outlet end of the blade is greater than one-half of the blade width L.sub.ax, with the inlet angle .alpha..sub.1 being in the range of between 35.degree.-40.degree., and the outlet angle .alpha..sub.2 being in the range of 25.degree.-28.degree.. A ratio of a narrowest width S.sub.2 of the flow channel at the blade outlet end to a narrowest width S.sub.1 of a flow channel defined between a back side of the blade in vicinity of the crossing point and a front side of an adjacent blade is 0.81.ltoreq.S.sub.2 /S.sub.1 &gt;0.96. A ratio of a distance l.sub.ax between a line connecting the outlet ends of adjacent blades and a line passing through the crossing point of the blade width L.sub.ax is in a range of 0.5-0.54, with a ratio of a distance L.sub.m from the outlet end of the blade to a maximum projecting point of a back side of the blade in a direction of rotation of the blade to the width L.sub.ax is in a range of 0.75-0.89. Additionally, a ratio of a distance from the maximum projecting point to a line connecting the outlet ends of adjacent blades is in a range of 0.6-0.66. By virtue of the above noted features of the present invention, a flow channel defined between the blades does not exhibit any great change in configuration downstream of the flow direction changing point thereby ensuring a minimization of a blade profile loss.
In accordance with further advantageous features of the present invention, the surface of a back side of the blade defining the flow channel is substantially straight at a portion thereof which is downstream of a portion thereof in a vicinity of the crossing point so as to avoid acceleration of the fluid flow along the back side of the blade.
Advantageously, the crossing point may be located in the position in which the distance between the crossing point and outlet end of the blade is less than four-fifth the blade width.
With a turbine blade constructed in accordance with the above noted features, it is possible to utilize such blade in a subsonic range.
Furthermore, with a turbine blade having a width ratio S.sub.2 /S.sub.1 within the range of 0.81 to 0.96, a flow velocity differential between the fluid flowing along the backside of the blade and the fluid flowing along the front side of the blade can be reduced. Accordingly, it is an object of the present invention to provide a turbine blade structure of high performance which reduces the downstream velocity defect of a turbine blade by minimizing the flow velocity differential between the fluid flowing along the front side of the blade and the fluid flowing along the back side of the blade.
A further object of the present invention resides in providing a turbine blade structure of a low blade profile loss.
Yet another object of the present invention resides in providing a turbine blade construction which is suitable for use in a subsonic range.
A still further object of the present invention resides in providing a turbine blade which is simple in construction and therefore relatively inexpensive to manufacture.
Yet another object of the present invention resides in providing a turbine blade which avoids, by simple means, shortcomings and disadvantages encountered in the prior art.
These and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, several embodiments in accordance with the present invention.